Generally speaking, the board upturn is defined as being the part of the ski located between the contact line, defined in a standardized way, and the extreme point of the ski. The board upturns are generally known as the “tip” and the “heel” when referring to the front and rear ends respectively.
The trend towards shortening the boards to make them easier to handle, combined with adapting them for skiing in powder snows, has led to specific geometries being defined for the tip and the heel.
Formerly, and as described in the document DE2556841, skis had a dimension line which they presented at a point of maximum width substantially at the level of the front contact line, this width gradually reducing beyond the front contact line in order to form the tip. After that, in order to improve lift, there has been a tendency to push the point of maximum width of the board forwards so that it is, as shown in the document EP 1 410 826 beyond the front contact line.
However, this tip (or indeed heel) widening, dictated by considerations of lift, may have negative consequences on the behavior of the board. Indeed, conventionally, a ski comprises an internal structure consisting of a core which intrinsically lacks any high strength mechanical properties, but which allows separation from the neutral fiber of the mechanical enforcement layers. These reinforcement layers may be varied in nature, and made on the basis of metal or fibrous reinforcements impregnated with a heat-setting resin. For practical reasons related to facilitating the manufacturing process, the reinforcement layer is often extended to the end of the tip. This construction does however have one major drawback in the case of skis for which the point of maximum width is located forward from the front contact line. Indeed, the increased surface of the tip for skis of this type means that the presence of the reinforcement layer increases the rigidity thereof, both flexurally and torsionally. The clear advantage in terms of lift on powder snows therefore turns into a disadvantage in respect of harder snows, since, because of its rigidity, the tip may alter the required deformation particularly when engaged on a turn.
One solution has been proposed in the document EP1 902 758 which comprises making a slit at the end of the ski to allow the differentiated deformation of the two sides of the tip. This solution is not really satisfactory, in that it slightly reduces the torsional value of the tip and it has almost no impact on its flexural rigidity. Additionally and above all, the mechanical complexity of such a solution is a significant source of fragility for the ski, making it very difficult to use.
Another attempted solution has been proposed for surfboards in the document WO 00/38801. This solution comprises interrupting the core in the upturn zone of the board end so that only the reinforcement layers are retained beyond. The presence of these reinforcements, even closer to neutral fiber, maintains a high level of rigidity in the tip.
The invention therefore sets out to improve the flexural and torsional stiffness behavior of skis which have a tip described as wide, in other words which gets wider beyond the front contact line.